Method of joining components of an aircraft structure

ABSTRACT

Two components of an aircraft structure are joined by providing a threaded opening in one of them and supporting an alignment insert in that opening. The alignment insert is used to guide drilling of the second component such that a hole is produced which is aligned with the threaded opening, for instance using an alignment projection which physically guides a drill. The alignment insert may then be removed. A fastener is then inserted through that hole and into the threaded opening, then tightened to form the completed joint.

CROSS RELATED APPLICATION

This application claims priority to United Kingdom Patent ApplicationGB2116100.5 filed Nov. 9, 2021, the entire contents of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The present disclosure relates to the field of aircraft manufacture.

The present invention concerns methods of joining components of anaircraft structure. More particularly, but not exclusively, thisinvention concerns joining first and second components using a threadedfastener, after using an alignment insert located in a threaded bore toguide the drilling of a second component to be joined thereto so thatthe hole in that component is aligned correctly. The invention alsoconcerns a kit of parts for performing such a method, an aircraft orpart of an aircraft produced using the method and/or the kit of parts,and a method of attaching a first part of an aircraft structure to asecond part of an aircraft structure.

Threaded fasteners such as bolts are used routinely when joiningcomponents during the manufacture of aircraft. Conventionally suchfasteners are used by jigging together the components to be joined,match drilling them, inserting the fastener through the hole and into anut, then tightening the nut and fastener to secure the joint. However,this requires access on both sides of the joint to tighten the fastener.In some spaces, for instance when the fastener passes into the wing tankof the aircraft, that access may not be possible (or conversely manyconstraints may be placed on aircraft design if they must be shaped toallow access on both sides). In other situations access may be possible,but may require those assembling the aircraft to work tight spaces or inother ergonomically difficult conditions such as spaces with difficultingress/egress points.

This need for access can be mitigated by providing one of the componentsto be joined with a threaded opening, for instance by tapping a hole init or by attaching a nut to it. However, this approach requires holes tobe formed in the other components which align precisely with thatthreaded opening so that the fastener can pass through the holes andinto the threaded opening before being tightened. Manufacturingvariation can lead to those holes being misaligned, leading to wastageor requiring ad-hoc adjustments to be made to compensate.

This problem, in turn, can be addressed by positioning the components intheir desired position, for instance using jigs and the like, drillingthem, then disassembling them to form the threaded opening. Particularlyfor larger pieces of aircraft structure this procedure can be veryarduous, adding considerably to overall production time. Further, insome cases it is possible for components to shift position slightly atsome point during the drilling, disassembly, opening forming andreassembly process, resulting in misaligned holes once again.

The present invention seeks to mitigate one or more of theabove-mentioned problems. Alternatively or additionally, the presentinvention seeks to provide an improved or alternative method of joiningfirst and second components of an aircraft structure, kit of parts,aircraft or part of aircraft, and method of attaching a first part of anaircraft structure to a second part of an aircraft structure.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a methodof joining first and second components of an aircraft structure, themethod comprising:

providing a threaded opening in the first component;

attaching an alignment insert to the threaded opening;

locating the second component in a required position relative to thefirst component;

using the alignment insert to guide drilling of a hole in the secondcomponent; and inserting a threaded fastener through the hole in thesecond component and into the threaded opening, and tightening thefastener to join the first and second components.

This method can avoid the need for the components to be positioned,drilled, then disassembled to form the threaded opening and thenreassembled. It can therefore allow for more time-efficient, and thuscheaper, production of aircraft structures. Further, the guidanceprovided by the alignment insert can reduce or eliminate the risk of thehole in the second component being misaligned with the threaded opening,thereby reducing or eliminating the wastage or lost time discussedabove.

The first component may be, for example, a fitting for a wing pylon suchas an upper fitting positioned in a wing tank. The second component maybe, for example, a wing skin.

The alignment insert may be threaded, and screw into the threadedopening to attach thereto. As an alternative, the alignment insert mayhave a cylindrical portion sized to tightly engage the threaded openingand be retained under friction.

The fastener may have an integral head, for instance the fastener may bea bolt or a machine screw. In such a case, tightening the fastener maycomprise inserting the fastener further into the threaded opening untilit is tight. As an alternative, the fastener may be a threaded stud witha nut, whereupon tightening the fastener may comprise moving the nutalong the threaded stud until it is tight, instead of or as well asinserting the stud further into the threaded opening.

The drilling of the second component may be controlled so that it doesnot travel beyond a predetermined point, i.e. so that the drill does notover-penetrate. This control may be provided in any suitable fashion,for instance through electronic servo-control, via visual feedback orusing abutting stop surfaces.

Said components may be parts of a wing assembly.

For example, the first component may be a fitting such as a fitting foran engine pylon, and the second component may be a skin of the wing ofthe wing assembly. As another example, the first component may be afitting for a flap assembly and the second component may be a wing spar.

The wing assembly of an aircraft may be a part where it is particularlydifficult to access both sides of a joint. Accordingly, the advantagesdiscussed above may be of particular benefit.

As an alternative, said components may be part of a tail assembly, arudder assembly or a landing gear structure, for example.

The step of providing a threaded opening in the first component mayinclude fixing a nut to the first component.

For instance, the nut may be a captive nut which may for example bepress-fitted into a hole in the first component.

This can be more time-efficient and/or offer a stronger joint than otherways of providing a threaded opening, for instance tapping a hole in thefirst component.

Optionally:

the method further comprises match-drilling the first component and athird component to form holes therein;

the threaded opening is provided in said hole in the first component;and

said fastener is inserted into the threaded opening through said hole inthe third component as well as through the hole in the second component.

The match-drilling operation can ensure that the hole in the thirdcomponent is aligned correctly with the location on the first componentwhere the threaded opening will be provided, without requiring the thirdcomponent to be drilled under guidance from the alignment insert (whichmay be slower and/or may place additional constraints on the design ofthe alignment insert or associated components).

The third component may be, for example, a further fitting for a wingpylon such as a lower fitting.

The fastener may be inserted into the threaded opening through said holein the third component and then through the hole in the secondcomponent. As an alternative, the fastener may be inserted into thethreaded opening through the hole in the second component and thenthrough the hole in the third component.

In other embodiments with a third component, the second and thirdcomponents may be processed together (for example they may be securedtogether in their required positions and drilled as one, under guidanceof the alignment insert). In such a case the joint may be considered tohave first, second and third components, or may alternatively beconsidered to have a first component, and a second component made up oftwo parts.

For the avoidance of doubt, in other embodiments with a third component,the third component may be drilled (where necessary) in any othersuitable fashion. For example, it may be provided with a slot or a setof holes so as to accommodate potential alignment, or may be drilledafter drilling of the second component, using the hole in the secondcomponent as a guide.

The method may further comprise attaching an alignment projection to thealignment insert so that the alignment projection can extend through apilot hole in the second component, the alignment insert guiding thedrilling of the second component via the alignment projection.

The alignment projection extending through the pilot hole can make thealignment projection, and thus the guiding action provided by thealignment insert, more accessible. For example, a component forassisting with drilling alignment which would not fit within thethreaded hole and/or the pilot hole may be provided on the distal end ofthe alignment projection as discussed below.

As an alternative, the alignment insert may have an alignment projectionintegrally formed therewith. As another alternative, no alignment insertmay be provided. In such circumstances the second component may or maynot have a pilot hole.

The alignment projection may be attached to the alignment insert beforeor after the alignment insert is attached to the threaded opening.

The alignment insert may support the alignment projection in a bore. Asan alternative, the alignment insert may have a protrusion received in arecess in the alignment projection.

The alignment insert may have a first thread for engaging the threadedopening, and a second thread for engaging the alignment projection, thefirst and second threads running in opposite directions.

In other words, the alignment insert may be attached to the threadedopening by rotating it in one direction, and the alignment projectionmay be attached to the alignment insert by rotating it in the oppositedirection.

This can allow the alignment insert to be removed from the threadedopening, for instance after drilling of the second component, by‘over-tightening’ the alignment projection (which may be moreaccessible) in a manner akin to a broken screw extractor.

As an alternative, the first and second threads may run in the samedirection. As another alternative, there may be no second thread and thealignment projection may engage the alignment insert in a differentfashion, for instance via an interference fit.

The alignment projection may physically guide the drill drilling thehole in the second component.

This can be an advantageously simple, and therefore quick, cheap and/orrugged way in which the alignment projection can guide drilling.

The drilling of the hole in the second component may be performed usinga drill which has an annular cutting edge encircling a central bore, thealignment projection being received within the bore of the drill duringsaid drilling.

This can be an advantageously simple, rugged or mechanically stable wayof physically guiding the drill, and/or one which is less vulnerable tovibration during drilling.

The alignment projection may engage the alignment insert via analignment projection thread, and the drill may rotate in the samedirection as the alignment projection thread.

In other words if the alignment projection thread is a right hand threadthen the drill rotates clockwise, or conversely if the alignmentprojection thread is a left hand thread then the drill rotatesanticlockwise.

This can avoid torque passed to the alignment projection from the drillthrough friction from unscrewing the alignment projection from thealignment insert. Instead, any torque transferred from the drill to thealignment projection may serve to tighten it.

As an alternative, the drill may rotate in the opposite direction to thealignment projection thread. In such a case the alignment projection maybe screwed into the alignment insert sufficiently tightly that anytorque from frictional engagement with the drill would not be sufficientto loosen it.

The central bore of the drill and the alignment projection may eachdefine respective stop surfaces, the stop surfaces abutting one anotherafter drilling of the second component so as to prevent the drill fromover-penetrating.

This can provide a simple and reliable way of preventing the drillover-penetrating (which may damage the alignment insert and/or thethreaded opening, for instance).

As some alternatives, over-penetration of the drill could instead beavoided using a manual depth stop contacting a surface of the secondcomponent which faces towards the drill, through appropriate depthcontrol of a CNC drill, or based on axial reaction force experienced bythe drill.

The stop surfaces may, for example, be respective end faces of the boreand the alignment projection. As an alternative, they may be respectiveshoulders provided part way down the bore and the alignment projection.

The drilling of the second component may use a drill comprising anannular cutting edge encircling a non-cutting projection, thenon-cutting projection passing through a pilot hole in the secondcomponent and being guidingly received in the alignment insert duringdrilling of the second component.

This can provide a simple and reliable way of guiding the drill withoutrequiring an alignment projection, which may be vulnerable to knockswhich may damage the alignment member, the alignment insert or the firstand/or second components. Instead or as well, the lack of need for analignment projection (or several alignment projections in the case ofmany joints being formed in parallel) can in of itself cut down on costsand/or eliminate any delay caused by the need to attach the alignmentprojection(s) to the alignment insert(s).

The non-cutting projection may be rotatable relative to the annularcutting edge. This can allow the non-cutting projection to rotate moreslowly, or not at all, when received by the alignment insert. This, inturn, can reduce wear and/or frictional heating produced by thenon-cutting projection rotating within the alignment insert.

In any method where the second component has a pilot hole, the pilothole may be at least 1 mm, for instance at least 2 mm or at least 3 mmsmaller than a diameter of the threaded opening (for instance themaximum diameter of the threaded opening, including the radial extentover which the threads are provided). Instead or as well, the pilot holemay be no more than 90%, for instance no more than 80% or no more than75% of a diameter of the threaded recess.

It can be advantageous for the pilot hole to be noticeably smaller thanthe threaded opening, since a greater degree of misalignment betweenpilot hole and threaded opening can be accommodated without the pilothole extending outside the footprint of the threaded opening (at whichpoint after drilling the hole in the second component would benon-circular).

The pilot hole may be no more than 6 mm, for instance no more than 5 mmor no more than 4 mm, smaller than the diameter of the threaded opening.Instead or as well, the pilot hole may be at least 40%, for instance atleast 50% or at least 60% of the diameter of the threaded opening.

It can be advantageous for the pilot hole to nonetheless be aconsiderable proportion of the side of the threaded opening. A pilothole that is too small relative to the threaded opening could mean thatless misalignment could be tolerated before an alignment projection thatis concentric to the threaded opening would be unable to project throughthe pilot hole.

The non-cutting projection may define a stop surface and the alignmentinsert or the first component defines another stop surface, the stopsurfaces abutting one another after drilling of the second component soas to prevent the drill from over-penetrating.

This can provide a simple and reliable way of preventing the drillover-penetrating (which may damage the alignment insert and/or thethreaded opening, for instance).

As some alternatives, over-penetration of the drill could instead beavoided using one of the methods described above.

The stop surfaces may, for example, be an end face of the non-cuttingprojection and a narrowed waist or a ‘roof’ provided in the alignmentinsert, in a nut attached to the second component, or in a nut cappositioned over such a nut.

The non-cutting projection of the drill may be axially movable betweenextended and retracted positions relative to the annular cutting edge,and the non-cutting projection moves from the extended position to theretracted position in the course of drilling of the second component.

Drilling beginning with the non-cutting projection in the extendedposition can allow more of the non-cutting projection to be received bythe alignment insert, and thus the guiding of the alignment insert to bestronger and/or more stable, before the annular cutting edge contactsthe second component.

The non-cutting projection moving to the retracted position duringdrilling can allow the length of travel of the annular cutting edge tobe greater than that of the non-cutting projection. This, in turn, canreduce the risk of the non-cutting projection “bottoming out” (on a stopsurface provided by the alignment insert or part of the first component,for example) before the annular cutting edge has fully penetrated thesecond component, thereby removing design constraints which wouldotherwise be placed on the drill and/or alignment insert.

The alignment insert may support an optical target structure anddrilling of the second component is performed by a drill using aguidance system, the guidance system controlling the path of the drillbased on orientation information provided by the optical targetstructure.

This can allow the method to be performed using existing precisiondrilling equipment set up to be aligned using an optical targetstructure, rather than requiring a plant to invest in new machinery (forinstance a drill with annular cutting edge encircling a central bore, ora drill with an annular cutting edge encircling a non-cuttingprojection, as described above) in order to perform the method.

As an example, the guidance system may identify a drilling axis based onthe position and orientation of one or more optical targets provided bythe optical target structure, and then move the drill along said axis todrill the second component. As an alternative, the optical targetstructure may include a laser diode emitting a laser beam along adrilling axis and the guidance system may use a movable light sensor todetermine the orientation of that axis and then move the drill alongsaid axis to drill the second component.

The optical target structure may, or may not, take the form of analignment projection as described above.

The alignment insert may support a magnet and drilling of the secondcomponent may be performed by a drill which using a guidance system, theguidance system controlling the path of the drill base on a sensedlocation of the magnet.

This can allow the method to be performed using existing precisiondrilling equipment set up to be aligned to drill towards a magnet,rather than requiring a plant to invest in new machinery (for instance adrill with annular cutting edge encircling a central bore, or a drillwith an annular cutting edge encircling a non-cutting projection, asdescribed above) in order to perform the method.

As an example, the guidance system may drill a hole that is normal to asurface of the second component which faces away from the firstcomponent, in a direction which intersects the centre of the magnet.

Drilling of the second component may be performed by orbital drilling.

This can allow drilling of multiple different size holes to be performedusing a single drill, by varying the orbital motion of the cutting bit.Instead or as well, this form of drilling can be beneficial where thesecond component has a pilot hole, which may be misaligned, asconventional drilling techniques can be vulnerable to the drill bitslipping into the pilot hole rather than following its intended path.

The method may further comprise the step of removing the alignmentinsert from the threaded opening after drilling the hole in the secondcomponent and before inserting the fastener.

This can reduce parts wastage and/or provide a lighter joint.

As an alternative, insert might be short enough relative to the threadedopening such that it can be left in place and the fastener insertedbehind it.

The alignment insert may be attached to the threaded opening such thatit is recessed relative to a surface of the first component which facestowards the second component when joined thereto.

This may provide a space beneath the alignment insert into which a drillcan ‘break through’ without drilling into the alignment insert anddamaging it.

The alignment insert may be recessed behind said surface by at least 0.2mm, for instance at least 0.5 mm or at least 0.8 mm. Instead or as well,the alignment insert may be recessed behind said surface by no more than10 mm, for instance no more than 5 mm or no more than 2 mm.

As an alternative, the alignment insert may be flush with said surfaceor may even stand proud of said surface, in which case it may be cut bythe drill to some extent. The alignment insert may be a disposablecomponent which is discarded after a single drilling operation, or thealignment insert may be reusable despite having been damaged by previousdrilling (for instance it may be longer than necessary, so as to accountfor gradual shortening by drilling over successive uses).

In methods where the threaded opening is provided by a nut, the nut maybe fixed to the first component such that it is recessed relative to asurface of the first component which faces towards the second componentwhen joined thereto. This may provide a space beneath the nut into whichthe drill can break through without drilling into the nut and damagingit or loosening its fixing to the first component.

The nut may be recessed behind said surface by at least 0.2 mm, forinstance at least 0.5 mm or at least 0.8 mm. Instead or as well, the nutmay be recessed behind said surface by no more than 10 mm, for instanceno more than 5 mm or no more than 2 mm.

The method may further comprise the step of applying a cover to thethreaded opening and/or the alignment insert, then applying a treatmentto the first component or to both the first and second components. Thetreatment may be applied before or after the second component is locatedin the required position. The treatment may be applied before or afterdrilling of the hole in the second component.

The treatment may be the application of a sealant. As an alternative,the treatment may be the application of a layer of primer or paint.

The method may further comprise removing said cover before curing of thetreatment.

The cover may protect the threaded opening and/or alignment insert fromobstruction of its proper function by the treatment. For instance, thecover may protect threads of the threaded opening and/or alignmentinsert so that the threads are not clogged by the treatment.

According to a second aspect of the invention there is provided a kit ofparts for performing a method according to the first aspect of theinvention, the kit comprising the nut, the alignment insert and thefastener, the alignment insert and the fastener each having threadsconfigured for engagement with the threaded opening of the nut.

The kit of parts may also comprise the first component and/or the secondcomponent. Instead or as well it may comprise, where present, analignment projection, drill, optical target structure and/or magnet asdescribed above. Instead or as well, it may comprise any other componentdescribed herein.

The kit of parts may enable a method according to the first aspect ofthe invention to be carried out, thereby providing one or more of theadvantages discussed above.

According to a third aspect of the present invention there is providedan aircraft or part of an aircraft, comprising first and secondcomponents joined using the method of the first aspect of the inventionand/or the kit of parts according to the second aspect of the invention.

An aircraft or part of an aircraft so produced can be cheaper due to oneor more of the advantages discussed above in relation to reduced wastageand/or faster production.

According to a fourth aspect of the present invention there is provideda method of attaching a first part of an aircraft structure to a secondpart of an aircraft structure, the method comprising:

providing a female set of threads on the first part;

mounting a drill guide to the female set of threads;

introducing the second part to the first part;

drilling a hole in the second part, in a position determined by thedrill guide;

inserting a joining member with a male set of threads into the femaleset of threads through the hole in the second part; and

tightening the joining member to clamp the first and second partstogether.

Also disclosed herein is a method of method of joining first and secondcomponents of an aircraft structure, the method comprising:

fixing a nut to the first component so as to provide a threaded openingtherein;

locating the second component in a required position relative to thefirst component; and

using a drill to drill a hole through the second component, in adirection towards the threaded opening.

The method may further comprise stopping drilling once the drill reachesthe first component, for instance before the drill touches the firstcomponent (for example the nut of the first component).

For the avoidance of doubt, the term ‘drilling’ is used herein todescribe the making of a hole, and is not intended to be otherwiselimited. Similarly, reference herein to a drill is used to describe atool which can make a hole. Tools and/or processes which make a hole aretherefore considered to be drills or drilling within the meaning usedherein. Accordingly, the term ‘drilling’ may be interpreted to mean ‘themaking of a hole’ and the term ‘a drill’ may be interpreted to mean ‘atool for making a hole’. Actions such as grinding and laser cuttingholes therefore constitute drilling, and the tools which perform thoseactions constitute drills.

It will of course be appreciated that features described in relation toone aspect of the present invention may be incorporated into otheraspects of the present invention. For example, the method of theinvention may incorporate any of the features described with referenceto apparatus of the invention and vice versa. Further, it is to be notedthat methods described herein are not intended to be limited to thesteps of those methods being performed in the order in which they arerecited. It would be readily apparent to the skilled person where stepscan, or cannot, be performed in a different order.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying schematic drawings ofwhich:

FIG. 1 shows a perspective view of an aircraft according to a firstembodiment of the invention;

FIG. 2 shows cross-sectional view of part of a wing assembly of theaircraft of FIG. 1 ;

FIG. 3 shows a cross-sectional view of a match drilling step of an upperfitting and a lower fitting of the wing assembly of FIG. 2 ;

FIG. 4 shows a cross-sectional view of the upper fitting of FIG. 3 ,with a captive nut attached thereto;

FIG. 5 shows a perspective view of an aligment insert for attachment tothe upper fitting;

FIG. 6 shows a cross-sectional view of the alignment insert of FIG. 5 ,attached to the captive nut of the upper fitting;

FIG. 7 shows a cross-sectional view of the upper fitting, with a lowerwing skin with a pilot hole introduced thereto;

FIG. 8 shows a perspective view of an alignment projection;

FIG. 9 shows a cross-sectional view of the alignment projection of FIG.8 , attached to the alignment insert and projecting through the pilothole of the lower wing skin;

FIG. 10 shows a cross-sectional view of a step of drilling the lowerwing skin under guidance of the alignment insert;

FIG. 11 shows a cross sectional view of the upper fitting and lower wingskin after drilling;

FIG. 12 shows a cross-sectional view of the upper fitting and lower wingskin after drilling of the lower wing skin, with the alignment insertand alignment projection removed;

FIG. 13 shows a cross-sectional view of the upper fitting, lower wingskin and lower fitting joined with a bolt;

FIG. 14 shows a perspective view of a drill for use in a secondembodiment of the invention;

FIG. 15 shows a cross-sectional view of an optical target structure foruse in a third embodiment of the invention;

FIG. 16 shows a side view of an optical target structure for use in afourth embodiment of the invention; and

FIG. 17 shows a side view of a magnetic target structure for use in afifth embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows an aircraft 1 according to an embodiment of the invention.It has a body 2, a tail 4 and two wing assemblies 5. Each wing assembly5 has an engine 6 mounted thereto via an engine pylon 7. The pylon 7 ofeach wing assembly 5 is mounted via a set of fittings.

FIG. 2 shows the fittings of one of the pylons 7 in situ, along with alower wing skin 8, upper wing skin 9 and front and rear spars 10 of theassociated wing assembly 5. There are two pairs of upper fittings 12towards the front of the wing assembly 5 (to the left from theperspective of FIG. 2 , one of each pair being hidden behind the frontspar 10) and a further pair of upper fittings 12 towards the rear of thewing assembly 5. Each pair of upper fittings 12 is joined to a lowerfitting 14, and to the lower wing skin 8 which is sandwiched between theupper and lower fittings 12, 14, by a set of threaded fasteners 16 inthe form of bolts. The pylon 7 is mounted to the lower fittings 14, andthus to the remainder of the wing assembly, by a pylon attachmentstructure (not shown).

It is noteworthy that the pair of upper fittings 12 towards the rear ofthe wing assembly 5 (and the upper fittings 12 which are hidden behindthe front spar 10) are positioned between the lower and upper wing skins8, 9, i.e. in the ‘wing tank’. This makes them difficult to be accessedby a technician, and thus conventional fasteners (which require accesson both sides of the joint) are not suitable for joining them to thelower skin 8 and lower fitting 14. Instead, they are joined using amethod according to the present embodiment, as described below.

Within the meaning of the present invention, each of the upper fittings12 towards the rear of the wing assembly 5 are examples of a firstcomponent, the lower wing skin 8 is an example of a second component,and the lower fitting 14 is an example of a third component. For thesake of clarity, only parts of said components are shown in thefollowing figures. Similarly, multiple similar joints are formed usingthe method to join these components, but the formation of a single jointwill be described below for the sake of clarity.

As illustrated in FIG. 3 , the first step of the method ismatch-drilling holes 20 in the upper and lower fittings 12, 14. Theupper and lower fittings 12, 14 are moved to the position relative toone another that they would occupy in the finished wing assembly 5, butbefore the components of the wing assembly 5 are assembled and accessbecomes difficult, then a drill bit 22 is passed through them to formholes 20 in those components which are correctly aligned with oneanother. In the case of the upper fitting 12, the hole 20 is made in ashoulder bushing 24 which has been press-fitted into an aperture in theupper fitting, whereas in the case of the lower fitting no such shoulderbushing is provided.

The next step is to form a threaded opening in the upper fitting 12. Inthis embodiment, as shown in FIG. 4 the threaded opening 26 is providedby a right hand female thread located in a nut cap 28 which is fixed tothe shoulder bushing 24, and thus to the upper fitting 12, therebyforming a captive nut 30 which in effect becomes part of the upperfitting. In this specific case the nut cap 28 is held in the shoulderbushing 24 by cross pins 32. The captive nut 30 has a roof 34 providedby the nut cap 28. The shoulder bushing 24, and thus the captive nut 30as a whole, is fixed such that it is recessed around 1 mm behind thelower surface 36 of the upper fitting 12.

At this point, a layer of sealant putty (not shown) is applied over thetop of the captive nut 30 so as to prevent any leakage of fluid (forinstance air, fuel or hydraulic fluid) through the upper fixing 12.

So that the lower wing skin 8 (and the lower fixing 14) can be joined tothe upper fixing 12, a hole must be drilled through it which is alignedwith the threaded opening 26 of captive nut 30 (and thus of the upperfitting 12). An alignment insert is attached to the threaded opening 26and used to guide the drilling of the hole in the lower skin 8 so thatthe hole is positioned correctly. FIGS. 5 and 6 show the alignmentinsert 40, in isolation and in situ in the captive nut 30, respectively.

The alignment insert 40 has a wider portion 42 and a narrower portion44. A first thread in the form of a right hand male thread 52 isprovided around the outside of the wider portion 42. A bore 46 runs upthe centre of the alignment insert 40. The part of the bore 46 withinthe wider portion 42 has a second thread in the form of a left handfemale thread 48, whereas the part of the bore 46 within the narrowerportion 44 is smooth. Said parts of the bore 46 meet at a shoulder 50.

Before the lower skin 8 is drilled, the alignment insert 40 is insertedinto the threaded opening 26, with the male thread of the alignmentinsert 40 engaging the female thread of the opening 26 so as to attachit. The alignment insert 40 is inserted until the end of the narrowerportion 44 contacts the roof 34 of the captive nut 30. In this position,the alignment insert 40 is recessed around 1 mm behind the lower surface36 of the upper fitting 12.

Also before the lower skin 8 is drilled, it is provided with anundersized pilot hole the purpose of which will be discussed below.Furthermore, in this embodiment a layer of sealant is provided betweenthe upper fitting 12 and the lower wing skin 8. To prevent the sealantseeping into the female thread 48 of the alignment insert 40, a cover inthe form of a plug (not shown) is inserted into the bore 46 so as tocover the thread 48.

With the cover (not shown) in place, a layer of sealant is applied tothe lower skin 8 and then the lower skin is moved to its requiredposition and secured in place using clamps or jigs. The cover is thenremoved, part way through the curing of the sealant, so the sealant isfirm enough to no longer seep into the threads 48, but not hard enoughto make removal of the cover more difficult. FIG. 7 shows the upperfixing 12 with the lower wing skin 8 in the required location, afterremoval of the cover.

As shown in FIG. 7 , the pilot hole 54 in the lower wing skin 8 ismisaligned with the threaded opening 26. More particularly, the axis 56of the pilot hole 54 is offset from the axis 58 of the threaded opening26. Accordingly, even if the pilot hole 54 was not undersized it wouldnot be possible to insert a fastener 16 (that was large enough to engagethe threads of the threaded opening 26) through the lower wing skin 8and into the threaded opening 26. However, the pilot hole 54 beingundersized means that the lower wing skin 8 can be drilled over the topof the pilot hole 54 but not concentric therewith, so as to enlarge thepilot hole to the required size and also shift the position of the holeso that it is aligned with the threaded opening 26. In this embodimentthe threaded opening has a diameter, including the diametric extent ofthe thread, of 12 mm whereas the pilot hole has a diameter of 8.5 mm,i.e. 3.5 mm smaller. In other words, the pilot hole 54 is around 70% ofthe diameter of the threaded opening. With the pilot hole being 3.5 mmsmaller in diameter than the threaded opening 26, the method of thisembodiment can accommodate the axis of the pilot hole 54 being offset byup to 1.75 mm. This amount of offset is what is shown in FIG. 7 .

As discussed above, the purpose of the alignment insert 40 is to guidethe drilling of the lower wing skin 8 to enlarge the pilot hole 54 andreposition it in alignment with the threaded opening 26. In thisembodiment, the alignment insert 40 guides the drilling via an alignmentprojection which is attached to the alignment insert 40, in thisparticular case after the lower wing skin 8 has been placed in therequired position, and projects through the pilot hole 54. FIGS. 8 and 9show the alignment projection 60, in isolation and attached to thealignment insert 40 respectively.

One end of the alignment projection 60 has an alignment projectionthread 62, which in this case is male left hand thread that iscomplementary to the female thread 48 of the alignment insert 40. Aformation 64 for engaging a driving tool, which terminates in an endface 68, is provided at the other end of the alignment insert 60. Anelongate shank 66 extends between the ends of the alignment projection60.

The alignment projection 60 is attached to the alignment insert 40 byinserting the end of the projection 60 with the thread 62 through thepilot hole 54 and into the bore 46 in the alignment insert 40, screwingit in (anticlockwise) to engage the thread 62 of the projection with thethread 48 of the insert 40, until it abuts the shoulder 50.

The alignment projection 60 of this embodiment physically guides thedrill which is drilling the lower wing skin 8. This is shown in FIG. 10. The drill 70 has an annular cutting edge 72 encircling a central bore74, in a manner akin to a hole saw. The central bore terminates in abottom surface 76. To drill the lower wing skin 8, the drill 70 isintroduced to the components 12, 8 in a manner which inserts theformation 64 and part of the shank 66 of the alignment insert 60 intothe bore 74. The shank 66 and bore 74 are a close fit, therefore thedrill 70 is constrained to move along the alignment projection. Thedrill is thus guided so that it remains in alignment with the threadedopening 26. The drill 70 continues to be advanced, inserting more andmore of the shank 66 of the alignment projection 60 into the bore 74 ofthe drill, and is rotated about its longitudinal axis. This moves therotating cutting edge progressively through the thickness of the lowerwings skin 8, drilling it.

Once the cutting edge 72 of the drill breaks through the upper surfaceof the lower wing skin 8, it enters the 1 mm gap beneath the alignmentinsert 40 which is provided by that component being recessed behind thelower surface of the upper fitting 12. At that point, the end face 68 ofthe alignment projection 60 abuts the bottom surface 76 of the bore 74of the drill. Those surfaces act as stop surfaces, preventing the drill70 from over-penetrating, i.e. travelling too far upwards and cuttinginto the alignment insert 40.

It is noteworthy that in this embodiment the drill 70 is rotatedanticlockwise, i.e. in the same direction as the alignment projectionthread 62. Accordingly, any transfer of torque from the drill 70 to thealignment projection 62 acts to tighten the attachment of the alignmentprojection 60 to the alignment insert 40.

After the lower wing skin 8 is drilled, it has a hole 20 which is of thecorrect size for a fastener 16 to be inserted through it, and which isaligned with the threaded opening 26 such that such a fastener 16inserted through the hole 20 could then engage the threaded opening.This is shown in FIG. 11 . The alignment projection 60 and alignmentinsert 40 are then removed from the captive nut 30 to make room for sucha fastener 16. In this embodiment, both insert 40 and projection 60 areremoved in a single action, using a driver engaged with the formation 64to rotate the alignment projection 60 anticlockwise. This tightens theengagement between the alignment projection thread 62 and the femalethread 48 of the alignment insert. When sufficient torque is applied,the alignment projection 60 forces the alignment insert 40 to rotateanticlockwise, loosening the engagement between the male thread 52 ofthe insert 40 and the threaded opening 26 and backing the alignmentinsert out of the opening. The upper fitting 12 and lower wing skin 8,with the alignment insert 40 and alignment projection 40 removedtherefrom, are shown in FIG. 12 .

After drilling of the lower wing skin 8 and removal of the alignmentinsert 40 and alignment projection 60, the lower fitting 14 (with itshole 20 produced in the match-drilling discussed above) is reintroduced.A fastener 16 is then inserted through the hole 20 in the lower fitting,through the hole 20 in the lower wing skin 8 and into the threadedopening 26. The fastener 16 is then tightened within the threadedopening 26, clamping the three components together and completing thejoint as shown in FIG. 13 .

Other embodiments of the invention will be described below. It is to beunderstood that these embodiments are similar to the first embodiment,therefore only the differences will be described. Correspondingreference numerals denote corresponding features.

FIG. 14 shows a drill 80 which in a second embodiment of the inventionis used in place of the drill 70 described above. The drill 80 has anannular cutting edge 82 like the drill described above, but in this casethe annular cutting edge 82 takes a form similar to a milling cutter.The annular cutting edge 82 encircles a non-cutting projection 84 whichterminates in a domed end face 86. The non-cutting projection 84 canrotate relative to the cutting edge 82, and can also move axiallyrelative to the cutting edge 82 between an extended position, shown inFIG. 14 , and a retracted position in which it is partially receivedwithin the annular cutting edge 82. The non-cutting projection 84 isbiased to the extended position by a spring (not visible).

To drill the lower wing skin 8 in this embodiment, the drill 80 isintroduced to the components 12, 8 in a manner which inserts thenon-cutting projection 84 of the drill 70 into the bore 46 of thealignment insert 40 (which may be threaded as described above, or mayfor example be smooth-walled or ribbed). The non-cutting projection 84is a close fit with the bore 46 of the alignment insert 40, thereforethe non-cutting projection 84 can only be inserted into the bore 46 toany significant extent when the drill 80 (in particular the annularcutting edge 82) is correctly aligned with the alignment insert 40 andby extension with the threaded opening 26. Thus, by receiving thenon-cutting projection 84 the alignment insert 40 guides the drilling ofthe lower wing skin 8 directly. The drill 80 is rotated and advanced,inserting the non-cutting projection 84 further into the bore 46 of thealignment insert 40 and moving the cutting edge 82 progressively throughthe thickness of the lower wing skin 8. Due to the non-cuttingprojection 84 being rotatable relative to the cutting edge 82, andindeed the rest of the drill 80, while the drill 80 rotates thenon-cutting projection is held rotationally stationary by frictionbetween it and the bore 46.

Since the non-cutting projection 84 is biased to the extended position,drilling begins with it in that position. The non-cutting projection 84stays in the extended position as it is inserted deeper into the bore 46and as the cutting edge 82 begins to cut through the lower wing skin 8.Part way through the travel of the cutting edge 82 through the lowerwing skin 8, the end face 86 of the non-cutting projection 84 contactsthe shoulder 50 of the bore. The shoulder 50 prevents the non-cuttingprojection 84 from moving any further. As the drill 80 continues to beadvanced and the cutting edge 82 continues through the lower wing skin8, the non-cutting projection 84 moves backwards relative to the annularcutting edge 82 towards the retracted position, against its bias.

Once the cutting edge 82 of the drill breaks through the upper surfaceof the lower wing skin 8, it enters the gap beneath the alignment insert40 which is provided by that component being recessed behind the lowersurface of the upper fitting 12 as discussed above. Also at that point,the non-cutting insert reaches the retracted position and can move nofurther. The end face 86 of the non-cutting projection 84 and theshoulder 50 of the bore 46 then act as stop surfaces, with theirabutment preventing over-penetration of the drill 80.

In a third embodiment of the invention the alignment insert 40 supportsan alignment projection in the form of an optical target structure,which is shown in FIG. 15 . The optical target structure 90 has a shank92 and a head 94 which supports an optical target 96. The shank 92 ininserted through the pilot hole 54 in the lower wing skin 8 and into thebore 46 of the alignment insert 40 to attach the target structure 90 tothe alignment insert. The head 94 remains beneath the bottom of thelower wing skin 8, where it is visually accessible.

In the third embodiment the drill (not shown) is a CNC tool with aguidance system, and has a laser diode and light sensor. With the laserdiode generating a laser beam, the drill undergoes movement in a searchpattern until it identifies the position in which the laser beam strikesthe centre of the optical target 96 while perpendicular thereto (laserlight from the laser diode, reflected by the optical target 96, beingdetected most strongly by the light sensor when in that position). Whenit reaches that position, the guidance system records the path in spacealong which the laser beam is shining, and identifies that path as anaxis along which the lower wing skin 8 should be drilled. The opticaltarget structure 90 is then removed, and the guidance system controlsthe path of the drill so that the hole formed thereby is concentric withthe axis (and thus aligned with the threaded opening 26). Accordingly,in this embodiment the alignment insert 40 guides the drilling of thelower wing skin 8 in that the insert determines the position andorientation of the optical target 96 which, in turn, is used by theguidance system to determine the desired path along which drillingshould take place.

In this particular embodiment, the drill performs orbital drilling, i.e.drilling in which a cutting tool follows an orbital path around acentral axis (which in this case is the axis identified by the guidancesystem). The details of orbital drilling will be readily apparent to theskilled person therefore no further detail will be provided here.

FIG. 16 shows an alternative optical target structure 100, according toa fourth embodiment of the invention. Like that of the third embodiment,the target structure 100 of this embodiment has a shank 92 for insertioninto the alignment insert 40 through the pilot hole 54, and a head 94.In this embodiment the head 94 has a hemicylindrical extension 102 withtwo diagonally-positioned optical targets 96, each of which issurrounded by a shroud 104. The two optical targets 96 are positioned onthe centreline of the shank 92.

The optical target structure 100 of the fourth embodiment functions inmuch the same way as that of the third embodiment, except that the drilldetermines the positions of the two optical targets 96 in a manner akinto a laser rangefinder, rather than aligning itself with either one ofthem. Having calculated the positions of the two targets 96, theguidance system calculates the position of an axis which would intersectthem. This axis is also the centreline of the shank 92, and thus of thealignment insert 40 and the threaded opening 26. The axis thereforedenotes the path which should be followed by the drill when drilling thelower wing skin 8.

In a fifth embodiment of the invention, the alignment insert supports amagnetic target structure as shown in FIG. 17 . The magnetic targetstructure 110 has a shank 92 like the magnetic target structures of thethird and fourth embodiments, but rather than a head the shank has amagnet 112 on its end. The magnetic target structure 110 does notproject through the pilot hole 54 in the lower wing skin 8, but insteadis received fully within the bore 46 of the alignment insert.

The guidance system of the drill of this embodiment does not have alaser or light sensor, but instead has a magnetic tracker with a drillbit aperture. Further, the guidance system of this embodiment isseparate from the drill. With the magnetic target structure 110 inposition within the alignment insert 40, and the lower wing skin 8 inthe required location, the magnetic tracker is positioned in theapproximate location of the magnetic target structure. Sensors withinthe magnetic tracker analyse the magnetic field in that region and usethe data to ascertain the position of the magnet 112 then automaticallymove the drill bit aperture so as to align it with the magnet 112, inthe same manner as is used in drilling using a through skin sensor(“TSS”). The bit of a drill is then passed through the drill bitaperture and through the lower wing skin 8 to produce a hole alignedwith the magnet, and thus with the threaded opening 26.

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein. By way ofexample only, the above embodiments use threaded fasteners in the formof bolts, whereas in other embodiments each threaded fastener may takethe form of a threaded stud with a nut. In such embodiments, the step oftightening the fastener may be performed by screwing that nut up thestud. As another example, while in the first embodiment the alignmentprojection is inserted into the alignment insert through the pilot holein the lower wing skin, in other embodiments the alignment projectionmay already be in place and then the lower wing skin may be introducedand its pilot hole placed around the alignment projection. As a furtherexample, the shank of the alignment projection may include fluting inwhich swarf from the drilling process can be accommodated and alongwhich that swarf can be removed from the area being drilled. As anotherexample, the end face of the alignment projection of the firstembodiment may be domed so as to avoid the corners of the formationgouging the bottom surface of the bore of the drill.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood thatsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

The term ‘or’ shall be interpreted as ‘and/or’ unless the contextrequires otherwise.

1. A method of joining first and second components of an aircraftstructure, comprising: providing a threaded opening in the firstcomponent; attaching an alignment insert to the threaded opening;locating the second component in a required position relative to thefirst component; using the alignment insert to guide drilling of a holein the second component; and inserting a threaded fastener through thehole in the second component and into the threaded opening, andtightening the fastener to join the first and second components.
 2. Amethod according to claim 1, wherein said components are parts of a wingassembly.
 3. A method according to claim 1, wherein the step ofproviding a threaded opening in the first component includes fixing anut to the first component.
 4. A method according to claim 1, wherein:the method further comprises match-drilling the first component and athird component to form holes therein; the threaded opening is providedin said hole in the first component; and said fastener is inserted intothe threaded opening through said hole in the third component as well asthrough the hole in the second component.
 5. A method according to claim1, further comprising attaching an alignment projection to the alignmentinsert so that the alignment projection can extend through a pilot holein the second component, the alignment insert guiding the drilling ofthe second component via the alignment projection.
 6. A method accordingto claim 5, wherein the alignment insert has a first thread for engagingthe threaded opening, and a second thread for engaging the alignmentprojection, the first and second threads running in opposite directions.7. A method according to claim 5, wherein the alignment projectionphysically guides the drill drilling the hole in the second component.8. A method according to claim 7, wherein the drilling of the hole inthe second component is performed using a drill which has an annularcutting edge encircling a central bore, the alignment projection beingreceived within the bore of the drill during said drilling.
 9. A methodaccording to claim 8, wherein the alignment projection engages thealignment insert via an alignment projection thread, and the drillrotates in the same direction as the alignment projection thread.
 10. Amethod according to claim 8, wherein the central bore of the drill andthe alignment projection each define respective stop surfaces, the stopsurfaces abutting one another after drilling of the second component soas to prevent the drill from over-penetrating.
 11. A method according toclaim 1, wherein the drilling of the second component uses a drillcomprising an annular cutting edge encircling a non-cutting projection,the non-cutting projection passing through a pilot hole in the secondcomponent and being guidingly received in the alignment insert duringdrilling of the second component.
 12. A method according to claim 11,wherein the non-cutting projection defines a stop surface and thealignment insert or the first component defines another stop surface,the stop surfaces abutting one another after drilling of the secondcomponent so as to prevent the drill from over-penetrating.
 13. A methodaccording to claim 11, wherein the non-cutting projection of the drillis axially movable between extended and retracted positions relative tothe annular cutting edge, and the non-cutting projection moves from theextended position to the retracted position in the course of drilling ofthe second component.
 14. A method according to claim 1, wherein thealignment insert supports an optical target structure and drilling ofthe second component is performed by a drill using a guidance system,the guidance system controlling the path of the drill based onorientation information provided by the optical target structure.
 15. Amethod according to claim 1, wherein the alignment insert supports amagnet and drilling of the second component is performed by a drillwhich using a guidance system, the guidance system controlling the pathof the drill base on a sensed location of the magnet.
 16. A methodaccording to claim 1, wherein drilling of the second component isperformed by orbital drilling.
 17. A kit of parts for performing amethod according to claim 3, the kit comprising the nut, the alignmentinsert and the fastener, the alignment insert and the fastener eachhaving threads configured for engagement with the threaded opening ofthe nut.
 18. An aircraft or part of an aircraft, comprising first andsecond components joined using the method of claim
 1. 19. An aircraft orpart of an aircraft, comprising first and second components joined usingthe kit of parts according to claim
 17. 20. A method of attaching afirst part of an aircraft structure to a second part of an aircraftstructure, the method comprising: providing a female set of threads onthe first part; mounting a drill guide to the female set of threads;introducing the second part to the first part; drilling a hole in thesecond part, in a position determined by the drill guide; inserting ajoining member with a male set of threads into the female set of threadsthrough the hole in the second part; and tightening the joining memberto clamp the first and second parts together.